This invention relates to toner compositions for use in developing latent electrostatographic images and more particularly to toner compositions which exhibit long life in the electrostatographic process.
In the development of electrostatographic images, a toner composition is mixed with a carrier composition in order to impart the proper charge characteristics to the toner particles and also for the purpose of carrying the toner particles by a physical means to the surface which contains the latent electrostatic image. The carrier particles are generally much larger in particle size than that of the toner varying from perhaps 5 to 100 times larger depending upon the particular developer being employed. The toner is thus subjected to large forces in the development housing and in transit toward the imaging surface, which forces result in the particle size reduction of the toner particles. This creates problems because it not only provides a source for dirt made up of the fine toner particles but also changes the triboelectric character of the toner particles because of the reduction in size thereof and the impaction and adhesion to the carrier particles. On the other hand, for economic reasons it is desired to use customary particle size reduction techniques to achieve the desired particle size of the colorant filled resinous materials. Uniformity in particle size can be achieved subsequent to size reduction by standard classification methods. A problem encountered because of these objectives is that particle size reduction will also occur in the electrostatographic apparatus because the conditions therein are similar to that encountered in the size reduction apparatus. Thus, brittle failure of the toner particles together with size reduction occurs in the electrostatographic process. This size reduction during the electrostatographic process results in changes in both the triboelectric and charging characteristics of the toner particles with respect to the particular carrier materials employed in the process. That is, as the particle size reduction of the toner particles occurs, the charge to mass ratio on the particles increases thereby increasing the forces holding the size reduced toner particles to the carrier particles. This results in even more harsh impacts between the large size carrier particles and the toner particles either causing further reduction in the particle size or flattening of the particles out in a pancake fashion which tightly adhere to the surface of the carrier particles eventually resulting in reduction in the triboelectric characteristics.